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Geostationary satellites



 
 
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  #1  
Old November 7th 18, 10:04 AM posted to sci.astro.amateur
Gerald Kelleher
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Default Geostationary satellites

A satellite in a geostationary orbit is basically an extension of the Lat/Long system into space as a sat hanging over a particular longitude on the surface is much like any object at sea level or on top of a mountain, for although rotational speeds at different in terms of height, they remain rotating with the Earth.

The Earth has two distinct surface rotations so the satellites experience a drift if not corrected although engineers nor much anyone else recognises the Polar day/night cycle and its surface rotational cause as a function of the orbital motion of the Earth -

"There are two other, less serious, problems with geostationary satellites. First, the exact position of a geostationary satellite, relative to the surface, varies slightly over the course of each 24-hour period because of gravitational interaction among the satellite, the earth, the sun, the moon, and the non-terrestrial planets."

https://searchmobilecomputing.techta...nary-satellite

It is proper to speak of an orbital pole or a point on the Earth's surface where the maximum surface rotation arising from an orbital surface rotation reaches zero . A rough guide for maximum rotational speed of the surface is the broken line in this graphic -

http://afewbitsmore.com/img/2015_ecliptic.png

The rotational speed parallel to the orbital plane at the maximum equatorial circumference is, on average, about 68.17 miles per day so the satellites are picking this up just as observers on the ground picked up variations in the natural noon cycle.
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  #2  
Old November 7th 18, 04:05 PM posted to sci.astro.amateur
Chris L Peterson
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Default Geostationary satellites

On Wed, 7 Nov 2018 01:04:17 -0800 (PST), Gerald Kelleher
wrote:

A satellite in a geostationary orbit is basically an extension of the Lat/Long system into space as a sat hanging over a particular longitude on the surface is much like any object at sea level or on top of a mountain, for although rotational speeds at different in terms of height, they remain rotating with the Earth.


All geostationary satellites are at the same latitude: 0. That is,
directly above the equator.
  #3  
Old November 7th 18, 05:05 PM posted to sci.astro.amateur
Gerald Kelleher
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Default Geostationary satellites

The same surface rotation responsible for the variations in the natural noon cycle and isolated as the Polar day/night cycle (parallel to the orbital plane), is registered by geostationary satellites as a daily drift.

Nobody should waste the information where the Equation of Time correction which creates the average 24 hour day and consequently the Lat/Long framework combines with human engineering where a satellite hanging over the same longitude meridian also registers the same surface rotation.

The constant rate of daily rotation is based on the average 24 hour day as 'average' and 'constant' can be interchangeable in timekeeping and dynamical circumstances.



  #4  
Old November 7th 18, 10:03 PM posted to sci.astro.amateur
Martin Brown[_3_]
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Default Geostationary satellites

On 07/11/2018 16:05, Gerald Kelleher wrote:
The same surface rotation responsible for the variations in the
natural noon cycle and isolated as the Polar day/night cycle
(parallel to the orbital plane), is registered by geostationary
satellites as a daily drift.


No. To first order they sit above one point on the Earth's equator with
just a few minor purturbations mostly from the sun and the moon.

You can photograph them relatively easily with time exposures and an
untracked camera so that the stars trail and the faint geostationary
satellites do not. The clue is in their name *GEO*stationary.

Some nice time lapse images of the geostationary line of birds he

https://petapixel.com/2015/10/07/geo...ky-time-lapse/

The trick to observing them is catching them at the time of year when
they give optimum specular reflections of sunlight or a big scope.
For once you don't need to track the stars - they drift past.

https://www.calsky.com/?geosat=

--
Regards,
Martin Brown
  #5  
Old November 7th 18, 10:35 PM posted to sci.astro.amateur
Gerald Kelleher
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Posts: 1,382
Default Geostationary satellites

On Wednesday, November 7, 2018 at 9:03:37 PM UTC, Martin Brown wrote:
On 07/11/2018 16:05, Gerald Kelleher wrote:
The same surface rotation responsible for the variations in the
natural noon cycle and isolated as the Polar day/night cycle
(parallel to the orbital plane), is registered by geostationary
satellites as a daily drift.


No.


The Earth's rotation projected into space in terms of geostationary satellites which reflect longitudinal fixed position albeit at a greater height and a faster rotational speed is only one of two distinct rotations.

The satellite has a forward motion through space as the Earth has so it will register the orbital surface rotations just as ringed planets display a surface rotation parallel to the orbital plane aside from and addition to daily rotation. The 4 degree orbital surface rotation of Uranus and its rings provide the observational certainty (about 50 seconds in) -

https://www.youtube.com/watch?v=612gSZsplpE&t=58s


A satellite in an orbit circling the circle of illumination will see the North and South poles turn beneath that satellite as a reflection of both the forward motion of the Earth through space and the slow and uneven rotation of the surface parallel to the orbital plane -

http://www.msss.com/mars_images/moc/...mericas250.jpg

The Equation of Time reflects the same combination of surface rotations, one rotation asserted to be constant (daily rotation) and the other uneven (orbital surface rotation.

This is not a competition, if people want to follow the principles then so be it or they can call out from the shadows about imaginary perturbations.



  #6  
Old November 9th 18, 04:43 AM posted to sci.astro.amateur
Quadibloc
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Default Geostationary satellites

On Wednesday, November 7, 2018 at 8:05:54 AM UTC-7, Chris L Peterson wrote:

All geostationary satellites are at the same latitude: 0°. That is,
directly above the equator.


There are geosynchronous satellites with inclined orbits and a figure-eight ground
track. A constellation of such satellites could possibly provide communications
service to arctic or antarctic communities.

John Savard
  #7  
Old November 9th 18, 02:57 PM posted to sci.astro.amateur
Chris L Peterson
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Posts: 9,866
Default Geostationary satellites

On Thu, 8 Nov 2018 19:43:32 -0800 (PST), Quadibloc
wrote:

On Wednesday, November 7, 2018 at 8:05:54 AM UTC-7, Chris L Peterson wrote:

All geostationary satellites are at the same latitude: 0. That is,
directly above the equator.


There are geosynchronous satellites with inclined orbits and a figure-eight ground
track. A constellation of such satellites could possibly provide communications
service to arctic or antarctic communities.


Right. But he was talking about geostationary satellites- a special
case of geosynchronous satellites that are necessarily at an
inclination of zero.
  #8  
Old November 10th 18, 07:44 AM posted to sci.astro.amateur
Gerald Kelleher
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Posts: 1,382
Default Geostationary satellites

Geostationary satellites hang above a longitude meridian and orbit the Earth at the same rate as the planet turns in the direction of daily rotation. It stands to reason that the orbit of the satellite is basically an extension of the Lat/Long system into space so the Equatorial speed at sea level will be 1037.5 miles per hour and once 24901 mile rotation in 24.

https://www.youtube.com/watch?v=XzhVK09YReA

The central reference of the satellite is the Earth in front of it so although it will not pick up the surface rotation of the North South poles parallel to the orbital plane, it may catch the edge of the Antarctic Continent move annually.

It should have alerted people to the fact that we see the same thing when the Sun is a central reference as both rotations combine to create the variations in the natural noon cycle.

 




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